Friction false twisting

ABSTRACT

APPARATUS FOR FRICTION FALSE TWISTING IN WHICH A TWIST BARRIER COMPRISING A STATIONARY CYLINDRICAL PIN IS SO POSITIONED AT A DISTANCE OF THE ORDER OF 1/8 INCH FROM THE PERIPHERY OF THE OUTLET END OF A FRICTION FALSE TWIST TUBE WITH WHICH THE YARN BEING FALSE TWISTED MAKES FRICTIONAL CONTACT AND TO GUIDE MEANS AROUND OR THROUGH WHICH THE YARN IS WITHDRAWN FROM SAID TWIST TUBE THAT THE YARN MAY BE PARTIALLY WRAPPED AROUND SAID PIN WITH AN ARC OF CONTACT THEREWITH OF BETWEEN 60* AND 100*.

FRICTION FALSE TWISTING I Filed Jan. 22, 1969 I lnvenlof ,Fw pi /MmeA644 Ass United States Patent C 3,564,833 FRICTION FALSE TWISTING RoySpencer Holliss, Pontypool, England, assignor to Imperial ChemicalIndustries Limited, London, England, a corporation of Great BritainFiled Jan. 22, 1969, Ser. No. 792,981 Claims priority, application GreatBritain, Jan. 30, 1968, 4,777 68 Int. Cl. D02g 1/04; D01h 7/92, 13/08US. Cl. 57--77.4 1 Claim ABSTRACT OF THE DISCLOSURE The inventionconcerns improvements in or relating to friction false twisting.

The art of friction false twisting of yarns, by means of a rotatingtwist tube having flared end-portions, at least, composed of materialhaving a high coefficient of friction with the yarn, is relatively new.

The basic principles of the process are described, with particularreference to the bulking of synthetic polymeric filaments and yarns, andthe process and apparatus broadly claimed in the specifications ofBritish Letters Patent Nos. 797,051 and 801,335.

A difficulty that has been encountered rather more specifically infriction false twisting than in false twisting by means of conventionalspindles having twist-trapping pins or rollers, is that of twistbleeding, which term is used to define the occurrence of occasionallengths of yarn having, improperly, some residual twist followingde-twisting in the false twist sequence of twisting and de-twisting.

Such twist bleeding, which is randomly distributed within yarn from oneprocessing position, and between yarns from different processingpositions, is evident as an undesirable short-term flashiness (darkstreaks) in the resultant fabric, e.g. a weft-knitted fabric.

It has now been discovered that a critical amount of positive twisttrapping by means of a twist barrier closely spaced from the outlet ofthe friction false twisting tube used for bulking can lead to thevirtual prevention of twist bleeding, as evidenced by the disappearanceof flashiness in resultant fabric, without significant effect on thebulk of the yarn.

The amount of twist trapping is critical, because too little will notassist in overcoming the defect of twist bleeding while too much canhave the effect of virtually eliminating the bulk from the yarn.

According to the invention, therefore, in and for the process offriction false twisting, a twist barrier comprising a stationary pin isso positioned with respect to the outlet end of a friction false twisttube with which the yarn being false twisted makes frictional contactand to guide means around or through which the yarn is withdrawn fromsaid twist tube, that the yarn may be partially wrapped around said pinwith an arc of contact therewith of between 45 and 180 and that contactwith said pin is made by the yarn immediately after it has left contactwith said outlet end of said twist tube.

The invention also provides an apparatus for operating the above processof friction false twisting.

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Preferably the stationary pin is cylindrical and has a hardwear-resistant surface. Ceramic, bright chrome and matt chrome surfaceshave proved satisfactory.

An arc of contact of between 60 and is preferred, as within this rangetwist bleeding is minimised without damaging the yarn or its filamentsand without reducing the bulk in a yarn that has been bulked by thefriction false twisting process.

Below 60, the amount of twist bleeding begins to increase rapidly, sothat below 45 the extent of improvement is too marginal to beacceptable. Over 100, for example between 100 and the tension is such asto break any stray filaments, which is usually undesirable. Above and inparticular when a complete (i.e. 360) wrap is made around the pin, thetension is so high that the bulk is removed altogether.

By immediately after is meant that the stationary pin should bepositioned as closely to the outer periphery of the outlet end of thetwist tube as is possible consonant with remaining free from contacttherewith and with allowing threading-up of the twist tube and pin to beaccomplished readily. A distance of as little' as inch has provedsatisfactory; but even as close a distance as 3 inches has proved to berelatively ineffective in minimising twist bleeding.

The diameter of a cylindrical pin is not too critical, within the rangeof realistic diameters; but a small diameter, for example inch, ispreferred to a larger one, for example inch.

As an instance of the efficacy of the invention, the following detailedexamples thereof are given, though they should not be construed aslimiting the invention in anyway.

EXAMPLE I being composed of polyurethane having a inch inner diameter,flaring to an outer diameter of 2 inches, and short hardness 92 and 88respectively. The heater upstream of the twist tube was at a temperatureof 225 C., and the yarn was positively fed into and withdrawn from thetwist zone by draw rolls and take-out rolls, respectively, so as tounderfeed the yarn through the zone at an underfeed of 3.3% and aconcomitant tension of 19 grams. The tension downstream of the twisttube was 50 grams.

A stationary, cylindrical matt chrome pin of inch diameter waspositioned at a distance of inch from the outer periphery of thepolyurethane end-portion of the twist tube, such that the yarn made anarc of contact of 90 around it end route to the take-out roll.

The yarn so produced was satisfactorily bulked and gave no indication oftwist bleeding, as evinced by fiashiness, when made into a weft-knittedfabric.

EXAMPLE II With the same apparatus and stationary pin characteristics asdescribed in the previous example, a 150 denier/ 30 filament yarnderived from polyethylene terephthalate was false twist bulked at 1000feet/minute. The twist tube was rotated at 10,000 rpm. and the heaterupstream of the tube was at a temperature of 220 C. The yarn waspositively fed into and withdrawn from the twist zone by draw rolls andtake-out rolls, respectively, as above, so as to underfeed the yarnthrough the zone at an underfeed of zero percent and a concomitanttension of 25 grams. The tension downstream of the twist tube was 100*grams.

The yarn so produced was satisfactorily bulked and gave no indication oftwist bleeding, as evinced by flashiness, when made into a weft-knittedfabric.

Although the specific conditions may vary somewhat with other syntheticpolymeric yarns, the invention has been found to be equally effectivewith other polyamide and polyester yarns, for example, those derivedfrom polycaprolactam and polyethylene isophthalate, respectively, andwith yarns derived from such synthetic polymers as polyacrylonitrilesand polyolefines.

The accompanying diagrammatic drawing illustrates the invention.

In the drawing, yarns Y and Y are led slightly separated away from aheater (not shown and by which the twist is set) through guides 1, 3 tothe inlet end of two contra-rotating twist tubes 5, 7. As indicated, theyarns pass diagonally through the hollow twist tubes, making contact ateach end thereof with a bush of polyurethane, the outlet ones of whichare shown at 9, 11.

From the bushes 9, 11 the yarns are partially wrapped around stationarycylindrical pins, 13, 15, acting as twist barriers, the arc of contactbeing, for example 90. Both the yarns are then brought together on theperiph- 'ery of take-out roll 17, when they may be passed to eitherplying or separate wind-up stations (not shown).

What is claimed is:

1. Apparatus for friction false twisting in which a twist barriercomprising a stationary cylindrical pin is so positioned at a distanceof the order of inch from the periphery of the outlet end of a frictionfalse twist tube with which the yarn being false twisted makesfrictional contact and to guide means around or through which the yarnis withdrawn from said twist tube that the yarn may be partially wrappedaround said pin with an arc of contact therewith of between andReferences Cited UNITED STATES PATENTS 2,936,570 5/1960 Arthur et al.5777.4X 3,154,906 11/1964 Van Assendelft et a1. 5777,4X 3,204,396 9/1965Poster at al. 5734 3,330,104 7/1967 Dunwoody 57-512 3,439,485 4/1969Lloyd 57-34 DONALD E. WATKINS, Primary Examiner

